LETTER TO THE SECRETARY OF WAR. 31 
practicable lines from the Mississippi river north of the Missouri, and with at least one prac- 
ticable route to the Columbia. 
4. That the routes north of the Missouri will connect with the Missouri at the mouth of the 
Yellowstone, and at the falls by easily constructed and short spur roads. 
5. That the Missouri is navigable at all seasons, when not obstructed by ice, for some distance 
above Fort Union, and is believed to be navigable to the falls for steamers drawing 18 inches 
of water. 
6. That east of the Yellowstone, all the roads must pass over the broad plateau of the Bois 
de Sioux and the valley of the Mouse river. 
7. That roads may be run over the Bois de Sioux from several points on the Mississippi. 
8. That at least two good routes can connect the Bois de Sioux with the Mouse River valley— 
one in the direction of Dead Colt Hillock, on the general route pursued »y Lieutenant Grover, 
and one on the general route pursued by the main party crossing the Cheyenne river. These 
routes meet on the entrance into the Mouse River valley. 
9. That the Milk river route affords extraordinary facilities for a railroad connecting with 
all the passes, and that a route can be pursued between the Milk and Missouri rivers, running 
near Fort Benton and the falls, and naturally connecting with Cadotte’s Pass. 
10. That a natural valley, called the Grand Coulée, connecting the routes between the mouth 
of the Yellowstone and the mountains with the Mouse River valley, and that the passage of 
the Coteau du Missouri is of easy grade, 
11. That by a deflection from @adotte’s Pass along the valley of the St. Mary’s river, a road 
can be made to Clark’s fork of the Columbia, and by a somewhat circuitous route, and with 
expensive side cutting, can be extended to the head of navigation of the Columbia. 
WORK TO BE DONE DURING THE FALL AND WINTER. 
1. The route pursued by Lieutenant Saxton to be carefully examined by the estimating engi- 
neers, to collect the data for estimating the cost of the road. The profile to be tested by addi- 
tional barometrical observations, and additional observations to be made for latitude and longi- 
tude. The line to be straightened and improved by side reconnaissance. 
2. The survey of the Missouri to be continued to the falls, to determine its navigability for 
steamers, and the cost of removing the obstructions, to secure a greater depth of six to twelve 
inches. 
3. A pass to be searched for in the Bitter Root range, and a route to be explored from Cadotte’s 
Pass along the Little Salmon river to Wallah-Wallah, to connect with the survey already made 
by Captain McClellan, in laying out the military road from Wallah-Wallah to Nisqually. 
4, A route to be examined from Cadotte’s Pass by the Mission of St. Joseph, and passing over 
a somewhat difficult portion of the Bitter Root range, but much used by the Indians and half- 
breeds in passing from the mountains to Wallah-Wallah. 
5. A detached party under Lieutenant Arnold to leave the main party operating on Lieu- 
tenant Saxton’s line, and move to and beyond Fort Colville to the Cascade mountains, and thence 
along the eastern base to the line of the military road, to open a communication with Captain 
McClellan, and connect the surveys to the Columbia with the passes explored by him in that 
range. 
6. Winter posts at Fort Benton and St. Mary’s, under the charge of Mr. Doty and Lieutenant 
Mullan, to make meteorological and magnetic observations, surveys of the country along the 
base of the mountains, and into the entrance of the several passes, to collect information as to 
these passes from guides and Indians, in readiness for operations in the spring. In addition to 
which, attention to be given to collections and to the Indian tribes. 
7. The survey of the mountain passes in winter by Lieutenant Grover, going with a dog 
train over all the ranges from Fort Benton to Puget sound. 
